Delita was manipulating her. She was the means to his ascension to power. He cared nothing for her personally. As soon as she outlives her usefullness and becomes a possible threat to him, he kills her with no remorse.
To be fair, she attacked him. And he did look quite remorseful afterwards, you don't look to the sky and muse about what your life could have been right after you get everything you have been dreaming of.

If he really wanted to kill everyone who was a threat to him he would have killed Olan and Balmafula. He had nothing to gain by leaving them alive, they were only a potential liability.